Open Data supplied by Natural Environment Research Council (NERC)

Niskin Bottle

The Niskin bottle is a device used by oceanographers to collect subsurface seawater samples. It is a plastic bottle with caps and rubber seals at each end and is deployed with the caps held open, allowing free-flushing of the bottle as it moves through the water column.

Standard Niskin

The standard version of the bottle includes a plastic-coated metal spring or elastic cord running through the interior of the bottle that joins the two caps, and the caps are held open against the spring by plastic lanyards. When the bottle reaches the desired depth the lanyards are released by a pressure-actuated switch, command signal or messenger weight and the caps are forced shut and sealed, trapping the seawater sample.

Lever Action Niskin

The Lever Action Niskin Bottle differs from the standard version, in that the caps are held open during deployment by externally mounted stainless steel springs rather than an internal spring or cord. Lever Action Niskins are recommended for applications where a completely clear sample chamber is critical or for use in deep cold water.

Clean Sampling

A modified version of the standard Niskin bottle has been developed for clean sampling. This is teflon-coated and uses a latex cord to close the caps rather than a metal spring. The clean version of the Levered Action Niskin bottle is also teflon-coated and uses epoxy covered springs in place of the stainless steel springs. These bottles are specifically designed to minimise metal contamination when sampling trace metals.

Deployment

Bottles may be deployed singly clamped to a wire or in groups of up to 48 on a rosette. Standard bottles have a capacity between 1.7 and 30 L, while Lever Action bottles have a capacity between 1.7 and 12 L. Reversing thermometers may be attached to a spring-loaded disk that rotates through 180° on bottle closure.

CTD bottle samples of nutrients, TDN and DOC collected on cruise D253 along Extended Ellett Line

Originator's Protocol for Data Acquisition and Analysis

A large scale CTD survey of the Iceland Basin and Rockall Trough was carried out during this cruise along the Extended Ellett Line, comprising a total of 153 CTD casts.

To determine nutrients, samples were drawn from all depths at all stations, with the exception of stations 14024, 14025 and 14026, directly into virgin polystyrene coulter counter vials. Samples were then stored in a fridge before analysis, which was generally commenced within 12 hours. The concentrations of nitrate + nitrite, phosphate and silicate were then determined using conventional colorimetric methods using a Skalar San Plus autoanalyser. Further details are in Allen (2001), pages 146 to 153.

TDN (Total Dissolved Nitrogen) and DOC (Dissolved Organic Carbon) were determined by high temperature oxidation- further details on pages 170 to 171 of Allen (2001).

Instrumentation Description

The samples were taken with a CTD frame with 24 position rosette and 24 Niskin bottles. Nutrients were analysed with a Skalar San Plus autoanalyser.

BODC Data Processing Procedures

Data were received at BODC in the form of pstar format sample files, and various spreadsheets containing nutrient, chl-a, TDN and DOC measurements. Bottle metadata were derived from the pstar files as these recorded rosette position and pressure, whereas some spreadsheets only recorded the nominal depths of bottle firing. Having combined the two data sources, the data were loaded into the BODC database using established BODC data banking procedures.

Where no pressure or depth information could be found from any source, a small number of bottles and measurements from them were discarded.

Parameters from the originator's source files were mapped to BODC parameter codes as follows:

Originator's Parameter

Unit

Description

BODC Parameter Code

BODC Unit

Comments

no2+3

µmol/l

Nitrate and nitrate from bottle sample determined by Auto Analyzer

NTRZAATX

Micromoles per litre

n/a

sio3

µmol/l

Silicate from bottle sample determined by Auto Analyzer

SLCAAATX

Micromoles per litre

n/a

po4

µmol/l

Phosphate from bottle sample determined by Auto Analyzer

PHOSAATX

Micromoles per litre

n/a

TDN Total Dissolved Nitrogen

mM

TDN from bottle sample determined by high temperature oxidation

NTOTCOD1

Micromoles per litre

n/a

DOC Disslved Organic carbon

mM

DOC from bottle sample determined by high temperature oxidation

CORGCOF1

Micromoles per litre

n/a

Data Quality Report

No report provided by the originator, but information about data quality is included in Allen (2001).

Problem Report

No problem report.

bindepth

m

Depth of ADCP bin

DBINAA01

m

-

evelcal

cm s -1

Relative Eastward current velocity

LCEWAS01

cm s -1

Not in final file as absolute velocities are present

nvelcal

cm s -1

Relative Northward current velocity

LCNSAS01

cm s -1

Not in final file as absolute velocities are present

velvert

cm s -1

Vertical current velocity

LRZAAS01

cm s -1

-

velerr

cm s -1

Velocity error

LERRAS01

cm s -1

-

intense1

db

Beam 1 intensity

ASAMSP00

db

-

intense2

db

Beam 2 intensity

ASAMSP02

db

-

intense3

db

Beam 3 intensity

ASAMSP03

db

-

intense4

db

Beam 4 intensity

ASAMSP04

db

-

ve

cm s -1

Ship's Eastward velocity

APEWGP01

cm s -1

-

vn

cm s -1

Ship's Northward velocity

APNSGP01

cm s -1

-

absve

cm s -1

Absolute Eastward current velocity

LCEWAS01

cm s -1

-

absvn

cm s -1

Absolute Northward current velocity

LCNSAS01

cm s -1

-

lat

Degrees

Latitude

ALATGP01

Degrees

-

lon

Degrees

Longitude

ALONGP01

Degrees

-

distrun

km

Distance run

DSRNCV01

km

-

Reformatted data were visually checked using the in-house editor EDSERPLO. No data values were edited or deleted. Flagging was achieved by modification of the associated quality control flag to 'M' for suspect values and 'N' for nulls.

Once quality control screening was complete, the data were archived in the BODC National Oceanographic Database and the associated metadata were loaded into an ORACLE Relational Database Management System.

Please note:the supplied parameters may not have been sampled from all the bottle firings described in the table above. Cross-match the Sample Reference Number above against the SAMPRFNM value in the data file to identify the relevant metadata.